1. Field of the Invention
The present invention generally relates to measuring instruments and, more particularly, to automatic systems for analysis of particle size distribution of ground materials by a sedimentation technique.
The invention may be used for analysis of the granulometric composition of ground materials at concentration plants in ferrous and nonferrous metallurgy, in chemical industry and other industries producing or using dispersed materials.
2. Description of the Prior Art
Known in the art is an automatic system for analysis of the size of ground materials (USSR Inventor's Certificate No. 890157, IPC GO1 N 15/04, published Dec. 15, 1981) comprising a sedimentation cylinder filled with liquid, a device for sampling and delivery of the ground material in the form of a slurry to the sedimentation cylinder equipped with a sample input unit. The sedimentation cylinder is communicated with a measuring tube, in which the liquid level is measured by means of a level detector whose indications are used for analysis of the granulometric characteristic of the solid particles in the slurry.
However, mechanical destabilizing factors, including shocks, impacts, vibrations of the sedimentation cylinder, which are unavoidable under conditions of a production plant, result in a change in the liquid level in the sedimentation cylinder and the measuring tube and distort the results of the analysis of the ground product size.
Known in the art is an automatic system for analysis of ground material size (USSR Inventor's Certificate No. 1055998, IPC GO1 N 15/04, published Nov. 23, 1983) comprising a sedimentation cylinder filled with liquid and communicating with a measuring tube and a correcting tube, in which the liquid level is converted into an electric signal by means of elements sensing the liquid level. The sedimentation cylinder is provided with a sampling funnel. The liquid level sensing elements are connected through switches to a measuring oscillator with a frequency output. The percentage of solids in the given ground material sizes is determined by the nature of change of the liquid level in the measuring tube with time by a data processing and display unit. The prior art system includes a device for automatic error correction which eliminates the effect of the destabilizing factors on the analysis by monitoring the change of the liquid level in the correcting tube and the change in the time of connection of the liquid level sensing elements to the measuring oscillator. However, the automatic error correction device includes a controlled pulse generator producing pulses whose duration varies under the effect of an analog signal generated by said automatic device. This results in a low noise immunity of the known automatic system which hinders its utilization under conditions of a production plant characterized by a high noise level.
The apparatus, which in its technical essence and in the result obtained, is the closest to the claimed technical solution, is an automatic system for analysis of ground material sizes (U.S. Pat. No. 4,175,426, Int. Cl. GO1 N 15/04, publ. Nov. 29, 1979) comprising a device for sampling and delivery of a ground material in the form of a slurry, a sedimentation cylinder filled with liquid whose density is lower than that of the ground product, said cylinder having a funnel for introducing the ground material, the narrow outlet of said funnel being located within said sedimentation cylinder coaxially therewith; a differential circuit for measuring the mass of the ground material, which did not settle in the sedimentation cylinder at any instant of time of conduction of the ground material size analysis.
The prior art automatic system includes a reference cylinder communicating with the sedimentation cylinder. Both cylinders are identical and have attachments for filling them with a liquid to the same level, two pressure sensing elements located at the same level in bottom portion of the cylinder, a differential pressure sensor, a data processing unit whose data input is connected to the output of said differential pressure sensor while the timer inputs are connected to timer outputs.
The percentage of solid particles within the given sizes is determined by the character of a change with time of the pressure difference on the sensing elements in the reference and sedimentation cylinders after putting the sample into the sedimentation cylinder. However, in the prior art system the introduction of the sample into the sedimentation cylinder is effected directly from the circulating slurry stream. It is well known that in such a stream the particles of different sizes are segregated, i.e. the stream has different density along its length. Therefore, a small sample put into the sedimentation cylinder and localized in the stream does not reflect the granulometric composition of the slurry and is not representative. An increase in the volume of the sample fed into the cylinder is undesirable because it increases the amount of the introduced solid particles causing their hindered sedimentation (mutual influence on the settling speed), conglomeration of the particles and a respective inadmissible increase of the analysis error. The efficiency of the differential circuit is insignificant. This is due to the fact that the pressure sensing elements in the sedimentation and reference cylinders operate in a different way. In the reference cylinder the sensing element is in contact with pure water. In the sedimentation cylinder the pressure sensing element is in contact with solid particles. Therefore, these particles inevitably stick to the pressure sensing element and cause a change in its rigidity with respect to the pressure sensing element in the reference cylinder.